Electric-discharge system



March 28, 1961 F. E. BARsTow ETAL 2,977,509

ELECTRIC-DISCHARGE SYSTEM 2 Sheets-Sheet 1 Filed Sept. 17. 1959INVENTORS FREDERICK F. BARsTaw BYIRVING. F. ASTMAN ,47am/@Ys March Z8,1961 F. E. BARsTow ETAL 2,977,509

ELECTRIC-DISCHARGE SYSTEM 2 Sheets-Sheet 2 Filed Sept. 17. 1959 Nmo'mM/m /WTORNEYS United States Patent() ELECTRIC-DISCHARGE SYSTEMFrederick E. Barstow, Needham, and Irv-ing F. Eastman, Natick, Mass.,assignors to Edgerton, Germeshausen & Grier, Inc., Boston, Mass., acorporation of Massachusetts Filed Sept. 17,l1^,9.59\S1e11.,15km-840,591

7 claims. (m5315441) The present invention yrelates toelectric-.discharge systems and, 'though it is useful, also, rin moregeneral fields, it is particularly adapted for lsystems 'in which one ormore flash condensers or capacitors is or Yare discharged through thegaseous medium of a gaseous-discharge `device for such purposes as theproduction of a single ash of light or a repetition of flashes, as inashphotography, stroboscopic applications and the like.

For purposes of illustration, the klight-.flash-producing systems towhich the present invention is applied are of the type disclosed inUnited States Letters Patent No. 2,722,629 and 2,756,365, issued,respectively, on November 1, 1955, and July 24, 1956, to Kenneth J.Germeshausen, embodying normally ineffective voltage-.adding mechanisms,operative substantially simultaneously with the application of atriggering impulse `to a ash device, to boost the value of the voltageavailable for :discharging through .the flash device. AIt will `beevident, however, that the invention is also adaptable vto other typesof electric-discharge circuits, as well, such as those described inUnited States VLetters Patent Nos. 2,478,901 through 2,478,907., issuedAugust 16 1949, to Harold E. Edgerton.

In summary, the present invention is directed to safety, hold-olf, andvoltage-level-regulating systems land circuits, particularly ,adaptedfor apparatus of the above-described character, wherein protection isafforded for variations in voltage of the rflashing capacitor orcapacitors or failures in the same, and control is provided over thecapacitor char-ging rate and the tendency for the ilashing device tohold-'over its discharging following a flash.

An object `of the present invention, accordingly, is to provide a newyand improved electric system embodying such safety, 'hold-olf andvoltage-level-regulating circuits that automatically insure the properperformance characteristics of the system.

Other and further objects will be explained hereinafter and will be moreparticularly pointed out in connection with thc yappended claims.

The invention lwill now be described in connection with the accompanyingdrawings, Figs. 1 and 2 of which are schematic circuit diagrams of apreferred flashing apparatus, particularly emphasizing safety andhold-off features thereof, respectively.

In the drawings, positive and negative banks of parallel-connectedashing storage capacitors C1 and C, are shown connected in a seriesdischarge circuit between the anode 1 and cathode 2 of a three-electrodepreferably gaseous-discharge flash-tube device 3. The voltage lstored inthe-capacitor banks C1 and C7 is normally insuiiicient to producebreakdown and hence a discharge between the anode 1 and cathode 2 of thetube 3 in the absence vof a triggering stimulus applied to the triggerVelectrode 4. The device 3 may, for example, be of the various typesdescribed in the'said Letters Patent. A satisfactory deviceof thisnature, is, for example, thetype FX-29 xenon ash'tube marketed'byEdgerton, Germeshausen & Grier, Inc.

The capacitor banks C1 and C7 arecharged from upper l 380-800 cycle persecond generator, having phase lines f A, B and C and a ground Vline D.The phase lines of the source A, Band C, are, in turn, connected torespective pairs ofupower-leg windings A1-A2, B1-B2 and C1-C2 of aconventional magnetic amplifier switching circuit T1. Threevcontrolwindings C3, C 4 and C 5 `are provided, with the winding C3v connectedat its lower end to the ground terminal D and at its upper end, byconductorrS. to a terminal 5. l The control winding .C1V is connected byconductor 6 to the lower terminal of the capacitor bank C7, and byconductor 7, through a rectifier CR27 and a .resistanceR17, to the B-conductor line. Control winding C5 is connected by conductor 8 to aterminal 8 and by conductor 9 to a terminal 9.

As an example, kthe 'power-legrwindings A1-A2, B1-B2,` C1.C2 may have330 turns each. T-wo control windings may each have 500 turns, aresistance Vof ohms and a current requirement, for full control, of 7milliamperes; whereas the third control winding, for a purpose laterdescribed, may be 1000 turns, and have resistance of 360 ohms, and alesser full control-current requirement of 3.5 milliarnperes. Connectedto the right-hand ends of each .pair of the power-leg windings A1-A'2,B1-B2, C1C2, are oppositely-poled rectifers CR3-CR4, CRS-CR@.andCR7-CR8, as is well known, to control the current path through thewindings during each half cycle. See, for example, Transactions of theAmerican Institute of Electrical Engineers; Part I, September 195,2,Since the oper-ation of such `ampliiiers is widely understood, it willnot be explained herein in great detail other than to Ystate that therectiiiersr CRS-C114, CRS-CR and CR7-CR8, such as Type 303C Westinghousediodes, are respectively connected to Y-connected primary windings Pl,P2, P3 of a power transformer T2. The cooperative step-up secondarywindings S1, S2 and S3 of the power transformer T2, connect to terminalsIII, IV and V, with va common terminal connection VI. such as Type'1Nl127 Texas Instrument rectiiers, in series banks CR-9 through CR14connect the terminals III, IV and V to terminals I and II in order toprovide full-wave rectification for the B+, B- lines. As an example, a420-volt alternating-current output from the transformer T2 willproduce, at terminals I and II a 900-volt directcurrent voltage forcharging capacitor banks C1 'and Cr; `along the B+, B- lines. Thecapacitor banks, indeed,

may, for example, each comprise six parallel capacitors,

as shown of total capacitance value of about1750 microfarads.

Diodes CRS to CRS permit current to llow during the positive half ofeach cycle only through the upper windings A1, B1 and C1. During thenegative half of cach cycle, the diodes pass current through the lowerwindings A2, B2, C2. In this mode of operation, the special cores ineach winding are kept completely saturated, andy there is no restrictionto the rate of current flow. However, a small D.C. current applied toone of the three control windings C3, C4 and C5 will control directlythe ow of A.C. current in the power windings by driving the cores out ofsaturation. Current in the power windings will be restricted as itVtries to drive the cores back into saturation. By regulating ypowerinput to the stepup transformer T2, the control windings C3, C4 and C5establish the rate at which charging current flows into the`capacitor'banks C1.C7. The degree of A. C. control is directlyproportional to the amount of,D.-C..c urrent-which tlows. At 7 ma.,inthe above example, there" Diodes,

is maximum restriction to current flow in the power windings A1-A2,B1-B2, Cl-Cg. When current ows in the positive direction, say downwardin the control winding C3, positive control is exerted. However, ifcurrent in one of the control windings reverses, it will oppose thecontrolling effect of the other windings, prevented by series diodessuch as CR2 at terminal 5', and diode CR27, before mentioned.

As explained in the said Letters Patent, a gaseousdischarge switch VI ispreferred, for triggering the ashtube 3, the tube VI having an anode 9,a control electrode 10, a cathode 11 and a keep-alive electrode 12,connected through a resistance R11 to the terminal Vl. A plate Ytransformer winding L, is connected between the anode 9 and terminal VIand the cathode 11 is returned through a resistance R10 to the B- line.A capacitor C14, normally charged from terminals VI and II, throughcathode resistance R10, will discharge through the primaryrwinding L1and the tube V1, upon grounding of the control electrode 10. This maytake place by closing switch S, or any other initiating device orcircuit, connecting the electrode 10 through capacitor C15 to the groundterminal D. The secondary winding L2 then applies a negative pulse, say15,000 volts for several microseconds, to the trigger electrode 4' ofthe ilashtube 3. This reduces the firing voltage to approximately thepotential across the capacitor banks C1, C7. The discharge of capacitorC14, as explained in the said Germeshausen Letters Patent, causes thenormally ineffective secondary winding L3, the upper terminal of whichis connected to the flashtube cathode 2, to reinforce, supplement or addto the negative potential already at the cathode 2, further increasingthe potential between the flashtube anode 1 and cathode 2, and causingthe ashtube 3 to fire. A light flash of, say, one millisecond duration,more or less, will thus emanate from the tube 3. The network R14- C16connected between the upper terminal of L2 and the terminal VI acts asan isolation circuit at the grounded end of the high-voltage winding andis designed to prevent external arc-over from either electrode of theflashtube to the trigger winding. The before-mentioned cathode resistorR10 prevents the negative capacitor bank C7 from discharging through thetrigger tube V1.

A voltage regulating and level control circuit is also employedcomprising the rectifier CR1, such as a Zener diode, connected toterminal 9 and thus to the control winding C5 by conductor 9", andthence by conductor 8 to terminal 8 and the slider S of a potentiometerR5 (connected in -a bleeder network R4-R5R6 between terminals VI andB+), back through resistor R6. The heavy-shaded components CR1, C5, R4,R5, R5 and R2 thus serve to provide for control of the winding C5, thusto adjust the voltage applied to the capacitor banks C1, C7 by theslider S. ln addition, at some point of B+ voltage, the diode CRIexercises controlling or regulating action, keeping the lower terminalof winding C5 more negative than the upper terminal-such negativecurrent flow in C5 having a lessened elect upon the charging currentcontrol. If polarity reversal occurs, as the B- voltage approaches alimit, current Hows in the opposite direction in C5, regulating thebleeder current at R5.

The action just described is essentially that of a bridge circuit. Byvarying the tap-off S' at R5, the point at which the bridge balances canbe altered. Shifting the quiescent point changes the value of the -Bvoltage. Conversely, if the line voltage changes, the resultant changein -B voltage causes the magnetic amplifier T1 to reinforce or opposethe A.C. current as necessary to return the -B (and +B) voltages tonormal.

As before stated, one of the important features of the invention residesin a hold-off or quenching circuit that prevents continuous arcing afterthe flash tube 3 has fired, caused by suiciently high continued currentin the discharge circuit. This circuit is shown'in heavy lines in Fig.2. `With the capacitor banks C5C7 fully charged,

the terminals of the control winding C4 are both at the same potential.When, however, the flashtube 3 fires, the B capacitor bank C7 dischargesrapidly (in, say, one millisecond) and the upper terminal of C4 returnsto a near-zero potential. The long time constant of the network,consisting of C13, R7, and the control winding C4 combined with theisolating action of CR27, before-mentioned, result in holding the lowerterminal of C4 at a negative potential. With a difference in potentialacross its terminals, current ows through the control winding C4 fromthe upper to the lower terminal 3. As described earlier, positive D.`C.current ow in the winding limits the rate at which A.C. current ows,thus electively causing the magnetic amplifier T2 to isolate and thus,in effect, to disconnect power source A, B, C. The reduced current,thus, will not sustain arcing in the flashtube.

As the capacitor C13 discharges through R7, the control-winding negativecurrent will decrease, resulting in an increase charging current oncemore to the capacitor banks C7, C7-but at a time when there is no longerdanger of flashing hold-over in the tube 3, in view of the hold-offperiod, say of the order of tenths of a second, more or less, thatpermits the tube 3 to de-ionize.

The capacitor charging rate of the banks C7, C7 is controlled by acurrent-limiting circuit. In the normal mode of operation with theForm-Run switch S" in the Run position, shorting out resistor R15 in theB- line, the voltage drop across R16, in series therewith, which isproportional to the charging current, places a positive potential on theupper terminal of control winding C4 in relation to the lower terminal.The potential difference produces a positive D.C. current in the controlwinding C4 (from the upper to the lower terminal) which is lim-` ited bybefore-described resistance R17. The control current causes the chargingcurrent to be limited to the desired charging rate. Y

If the Form-Run switch is moved to the Form position, the larger voltagedrop creates a higher potential difference; considerably more currentows from the upper to the lower terminal of C4; maximum restriction isplaced on the charging current; and the voltage forms very slowly on thecapacitors C1-C7.

Because the before-described voltage-regulator circuit is only connectedacross the negative bank C7, a shortcircuit or other malfunction in thenegative circuit will produce an overvoltage on the positive bank C1.One of the circuits shown in heavy lines in Fig. l prevents thiscondition, as follows. Any decrease in voltage on the negative bank C7without a corresponding decrease in the positive bank C1 will cause theupper terminal of the control winding C4 to go positive in relation toits lower terminal. Positive current will ow through the control windingC4, thereby reducing the rate of voltage buildup on the capacitors tozero.

An unbalance in the B+ bank C7 does not endanger the B- bank C7 becauseof the protection afforded by the previously ldescribed voltageregulator across the B- bank, C7.` Because a B+ unbalance might reversethe current in the control winding and aggravate the unbalancecondition, the diode CR2 is inserted in circuit with the control windingC3 to prevent the reversal of current.

If, for any reason, the voltage on both banks C1, C7 becomes excessive,neon tubes V3--V10, indicated in heavy lines in Fig. l, and connectedbetween terminals I and 5', will ash over. The upper terminal of controlwinding C3 then becomes positive. A positive D.C. current will thus flowthrough the control winding C3 and the regulatory action will reduce thevoltage. The circuit may, for example, be designed to operate at950-1000 v.

Further modifications will occur to those skilled in the art and allsuch are considered to fall within thepspirit and scope of theVinvention as deiined inthe appended claims.

What is claimed is:

l. An electric flash-producing system having, in combination, anelectric flash device having a pair of principal electrodes and atrigger electrode, a source of energy, energy storage means, a chargingcircuit including switching means for storing voltage from the source inthe energy-storage means, a discharge circuit for the energy-storagemeans connected to the principal electrodes and including normallyineiective means for supplying voltage, when effective, in the dischargecircuit along with the voltage of the energy-storage means, means forsupplying a trigger impulse to the trigger electrode and substantiallysimultaneously rendering the normally ineiective means effective,thereby to enable the energy-storage means to discharge through thedischarge circuit in order to produce a Hash of energy between theprincipal electrodes of the Hash device, and means operable upon acomponent failure in the energy-storage means for controlling theswitching means to disconnect the said source from the energy-storagemeans.

2. An electric hash-producing system having, in combination, an electrictlash device having a pair of principal electrodes and a triggerelectrode, a source of energy, energy storage means, a charging circuitincluding switching means for storing voltage from the source in theenergy-storage means, a discharge circuit for the enorgy-storage meansconnected to the principal electrodes and including normally ineiectivemeans for supplying voltage, when eifective, in the discharge circuitalong with the voltage of the energy-storage means, means for supplyinga trigger impulse to the trigger electrode and substantiallysimultaneously rendering the normally ineifective means eifeotive,thereby to enable the energy-storage means to discharge through thedischarge circuit in order to produce a ash of energy between theprincipal electrodes of the ash device, and means responsive aftertheproduction of the ash of energy to current in the controlling theswitching means to disconnect the said Y source from the energy-storagemeans. l

3. Apparatus as claimed in claim 2 and inwhich means cooperative withthe said switchingmeans is provided for regulating the voltage suppliedfrom the said source to the energy storage means.

4. Apparatus as claimed in claim 2 and in which the last-named meanscomprises further energy-storage means, means operable upon theproduction of a dis-l charge through the ash device for discharging thefur-r ther energy-storage means, and means for controlling the switchingmeans in response to the discharging of vthe further energy-storagemeans to elect the said discon-A source of energy and theenergy-discharge device, magnetic amplifier means connected between thesource and the energy-storing circuit, and means responsive tosuiciently high current discharged through the discharge device andconnected to the magnetic amplier means to control the same to isolatethe said source from the energy-storage circuit. Y Y

7. Apparatus as claimed in claim 6 and in which the magnetic amplifiermeans is provided with control windfor continued current flow throughthe ash device for ing means and the isolating means comprises furtherenergy-storage means connected with the magnetic amplitierv controlwinding means in order to discharge therethrough. t f

References Cited inthe file` of this patent UNITED STATES PATENTS ParkerAug. 5, 1952l Y Edgerton Feb. 3, 1959

